1. Field of the Invention
The present invention relates to carbon nanotube (CNT) yarn-based surface field electron emitters and a method of fabricating the carbon nanotube yarn thereof. More particularly, the present invention relates to a method of fabricating surface field electron emitters based on electron emission from the surface of a carbon nanotube yarn upon application of an electric field to the carbon nanotube yarn, which is formed in an elongated wire shape having a diameter of several dozen to several hundred of micrometers by longitudinally aligning carbon nanotubes each having a diameter of several to several dozen nanometers.
2. Description of the Related Art
For electron emitters with a fine structure, carbon nanotubes or carbon nanowires are preferred as materials for electron emission. “Carbon nanotube” generally refers to a fine structure grown in a tube shape, and has a variety of kinds well known in the related art. The carbon nanotube exhibits excellent electrical, mechanical, chemical, and thermal properties, which allow the carbon nanotube to be applied in various fields.
The carbon nanotube has a low work function, a high aspect ratio, and a very large field emission factor due to a low radius of curvature at the top or emission end thereof so that the carbon nanotube can emit electrons even in an electric field of low potential.
As a conventional method of fabricating carbon nanotube field electron emitters, there are a method of forming a carbon nanotube directly on a conductor such as a cathode or substrate through vertical growth, and a method of attaching carbon nanotube powder to a cathode after synthesizing the carbon nanotube powder through a separate process.
Then, the carbon nanotube field electron emitters generally exhibit a phenomenon of emitting electrons from the tip end of the carbon nanotube upon application of an electric field thereto. In this regard, body emission of the carbon nanotube has been reported in recent years, that is, electrons are emitted from the surface of the carbon nanotube instead of the tip end of the carbon nanotube.
Furthermore, recent reports say that horizontally aligned carbon nanotube field electron emitters exhibit more stable and uniform field electron emission than vertically aligned carbon nanotubes.
However, it is very difficult to fabricate the horizontally aligned carbon nanotube field electron emitters, and, even if fabricated, fabrication efficiency is not satisfactory.
In a conventional method of fabricating a carbon nanotube yarn, a thin carbon nanotube strand is drawn out from a carbon nanotube, which is vertically grown on a silicon wafer, by Van der Waals' force exerted between edges of the carbon nanotubes when pulling the carbon nanotube from the edge of the carbon nanotube. Then, several carbon nanotube strands are plied, thereby providing the carbon nanotube yarn.
When an electric field is vertically applied to the diameter of the prepared carbon nanotube yarn, electrons are emitted from the overall surface of the carbon nanotube yarn, that is, from the body (or lateral surface) of the carbon nanotube yarn, as is opposed to the general carbon nanotube that emits electrons only from the tip end (edge) thereof.
However, the tip ends of the carbon nanotube strands protrude from the surface of the carbon nanotube yarn, thereby reducing field electron emission efficiency.
As such, since the ends of the carbon nanotubes protruding from the surface of the carbon nanotube yarn cause a reduction in field electron emission efficiency, it is necessary to form a smooth surface of the carbon nanotube yarn. Thus, for fabrication of the carbon nanotube yarn, conductive organic or inorganic binders, or polymer pastes are added to flatten the surface of the yarn. However, since this process is complicated and causes a cost increase, it is not generally applied in practice.